Field Testing the Single-Chip RollJam: Overcoming Near-Field Desensitization (Hardware vs Software solutions) 📡
Hey everyone, c0d3r_SubGHz here with a development update on the Single-Chip RollJam PoC.
Thanks to some incredible field testing from early adopters in the community, we ran into a fascinating physical limitation and found two ways to bypass it.
The Problem: Near-Field Desensitization Since the v1.0 uses a custom bare-metal SPI driver to blast Continuous Wave (CW) Jamming (a literal wall of RF fire) instead of the old TDM switching, the external module is extremely loud. Because the internal RX antenna and the external TX antenna are just an inch apart, the jammer effectively "blinds" the Flipper's internal receiver. It can't hear the target's keyfob over its own noise.
Here is how we are beating physics:
Solution 1: The Hardware Approach (See Picture 📸) As figured out by us, using an SMA extension cable to physically distance the jamming antenna from the Flipper's body prevents desensitization. The external module screams, the target car's AGC gets blinded, but the Flipper's internal radio stays clean enough to capture the rolling code.
Solution 2: The Software Approach (Jam Offset) If you don't want to carry cables around, I coded a dynamic 'Jam Offset' feature in the app's UI. By pushing the jamming frequency further away (e.g., +/- 120kHz to 900kHz from the center freq), you give the Flipper's internal receiver enough "breathing room" to catch the preamble, while still being close enough to corrupt the signal reaching the car's ECU.
Side note: I decided to keep the transition between Signal A and Signal B manual (requiring a button click) rather than auto-switching. This acts as a safety buffer so residual RF noise or bounced signals don't instantly trigger a garbage Signal B capture.
Massive thanks to the community for the data. Pushing the CC1101 hardware to its absolute limit is a fun ride.
(As always, due to subreddit rules, I don't post binaries here. Full documentation and project access are in my Bio/Profile).